The present invention generally relates generally to a projection apparatus for projecting a picture onto a screen, in a projection television receiver.
As shown in FIG. 1, a projection television receiver generally comprises a projection cathode ray tube 01 for reproducing a television signal or the like, a group of reflection mirrors 02 for reflecting light emitted from the projection cathode ray tube 01, a screen 03 for receiving reflected light so as to project an enlarged picture thereon, and a television receiver cabinet 04. The present invention particularly relates to an improvement of the projection cathode ray tube 01.
Referring to FIG. 1, the conventional projection apparatus in a projection television receiver will be described hereafter. FIGS. 2A, 2B, and 2C shows various examples of the apparatus such as that of FIG. 1. FIG. 2A shows an example of a projection apparatus having a projection cathode ray tube 021 and a lens 024 which are coupled to each other with silicone-gel. In this example, there have been problems of reduction in heat resistance, and generation of thermal transformation/distortion in the projection cathode ray tube 021 when the temperature at the projection face of the tube 021 has reached a high value. FIG. 2B shows another example of a projection apparatus in which a coolant A is disposed between a tube 021 and a lens 024 in order to prevent the generaton of heat by the projection cathode ray tube 021. In this example, the coolant A may evaporate or leak through a packing, thereby allowing the projection face of the tube 021 to reach a high temperature. Thus, there is still a potential problem of thermal transformation/distortion of the projection cathode ray tube 021. FIG. 2C shows a further example of a projection apparatus in which a projection cathode ray tube 021 and a lens 024 are spaced from each other in order to allow the heat from the projection cathode ray tube 021 to dissipate by air cooling. In this example, dust may adhere to the projection face of the tube 021 because of static electricity, or a transmittance loss may be caused because the image carrying light passes through materials having different refractive indices. Therefore a high-quality picture is not always obtained.
An object of the present invention is therefore to eliminate the foregoing disadvantages in the prior art.
Another object of the present invention is to provide a projection apparatus in a projection television receiver, in which a lens adjacent to a projection cathode ray tube is prevented from being transformed/distorted by heat from the projection cathode ray tube.
A further object of the present invention is to provide a projection apparatus in a projection television receiver, in which a cooling liquid for cooling the projection face of the projection cathode ray tube is prevented from leaking.
A still further object of the present invention is to provide an inexpensive projection apparatus in a projection television receiver, in which the transmission factor is maintained at a high level, and in which a high-quality picture having a high contrast ratio can be obtained consistently.
The above objects, features, and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.